1. Technical Field
The present invention relates to an electron emission display (EED) and, more particularly, to an electron emission display that controls a power sequence.
2. Related Art
A field emission display (FED), which is an electron emission display using a cold cathode, can be categorized into a field emitter (FE) type electron emission display, a metal-insulator-metal (MIM) type electron emission display, a metal-insulator-semiconductor (MIS) type electron emission display, a surface conduction electron emission display (SED), and a ballistic electron surface-emitting display (BSD).
In an FE type electron emission display, an emitter that facilitates electron emission due to an electric field in a vacuum is formed, and electrons are emitted from an emitter array. The emitter is formed of a material having a large β function (i.e., aspect ratio) and a small β function (i.e., work function).
An MIM type electron emission display or an MIS type electron emission display operates based on quantum mechanical tunneling, and employs an emitter including an MIM or MIS structure. In the MIM or MIS type electron emission display, a voltage is applied between both metal layers, or between a metal layer and a semiconductor layer, in which an insulator is inserted, so that electrons move from a metal layer or semiconductor layer having a high electric potential to a metal layer having a low electric potential.
A BSD operates on the principle that, if semiconductor size is reduced to a size range that is smaller than a mean free path of electrons in the semiconductor, the electrons are transported without scattering. The BSD includes an electron transporting layer (ETL), which is disposed on an ohmic electrode and formed of a metal or semiconductor, and an insulating layer, a thin metal layer, and a phosphor layer, which are disposed on the ETL. Thus, electrons are emitted by supplying power to the ohmic electrode and the thin metal layer so as to excite the phosphor layer, thereby emitting light.
In an SED, a current is horizontally supplied to the surface of a small-area thin layer disposed on a substrate so as to emit electrons, and a pair of a first electrode and a second electrode are formed on a first substrate so as to face each other. A first conductive layer and a second conductive layer are disposed adjacent to each other so as to cover the surfaces of the first and second electrodes, respectively. An electron emission unit is interposed between the first and second conductive layers. Also, Red (R), Green (G), and Blue (B) phosphor layers, each adjacent pair of which is separated by a black matrix layer, are alternately arranged on an anode above a second substrate.
In the SED, power is supplied to the first and second electrodes so that a current flows horizontally into the surface of the small-area electron emission unit. Thus, electrons are emitted from the electron emission unit and collide with the phosphor layers disposed on the anode, thereby creating a predetermined image.
Typically, an EED operates based on quantum mechanical tunneling, and involves a triode structure in which electrons are emitted due to an electric field formed by a gate electrode, and the electrons collide with phosphor layers formed on an anode to excite phosphors, thereby emitting light.
In the EED, if a predetermined driving voltage is applied to a cathode and the gate electrode, and a positive (+) voltage of several hundreds to several thousands of V is applied to the anode, an electric field is produced around an electron emission source due to a voltage difference between the cathode and the gate electrode, thereby emitting electrons. The electrons are transported toward the anode to which the high voltage is applied, and collide with corresponding phosphor layers so as to emit light. As a result, a predetermined image is displayed.
In driving a color FED, two kinds of addressing methods can be used, a switched anode method and a non-switched anode method.
In the switched anode method, a red (R) sub-pixel, a green (G) sub-pixel, and a blue (B) sub-pixel share a single FEA pixel, and all of the identically colored anode sub-pixels are electrically connected to one another. The switched anode method can employ a three times greater number of electron emission sources than the non-switched anode method, and the arrangement of anodes and cathodes is not very important. However, an anode voltage must be set to a certain value or less (mostly, 1 kV or less) to prevent color mixture caused by electrical breakdown between adjacent phosphor sub-pixels, and an anode voltage must be applied at a three times higher speed.
In the non-switched anode method, each sub-pixel uses an additional FEA sub-pixel, and three sub-pixels of a single pixel are electrically connected to each other. The non-switched anode method enables high-voltage operation since electrical breakdown hardly occurs between adjacent anode sub-pixels, and the method does not require conversion of an anode voltage at high speed. On the other hand, a three times greater number of gate electrodes than in the switched anode method are required. Also, since the number of electron emission sources used by each anode sub-pixel is small, each of the electron emission sources must supply a relatively large current. In addition, an alignment error between the anode and the cathode may affect color purity.
If a voltage is simultaneously applied to an anode, a gate electrode and a cathode, the anode voltage which has a rated voltage of approximately several kV is the last one to reach the rated voltage level. Accordingly, if the rated voltage is applied to the gate electrode and the cathode while the anode voltage has not yet reached its rated level, electrons emitted from the cathode are not accelerated toward the anode, but rather they flow into a gate, resulting in a leakage current. The leakage current may cut off the gate electrode, damage the electron emission sources, and waste power.